The invention deals with, for example, high-speed rotary atomizers suitable for the electrostatic mass-production coating of work pieces, such as vehicle chassis, with electrodes, which are used for external charging of the coating material and which in operation are at a high voltage on the order of magnitude of 100 kV, while the bell-shaped plate in the area of the electrode field should be at a defined potential, usually ground potential (EP 0 796 663 B1). However, it can also concern rotary atomizers with components, such as, e.g., the bell-shaped plate, which are charged to a high voltage (EP 0 801 991 A2).
Radial turbines, which are driven by compressed air in a known way and which have a hollow shaft that carries the bell-shaped plate and that rotates without contact in air bearings, are used for driving the bell-shaped plate of such atomizers. For potential neutralization between the hollow shaft with the bell-shaped plate affected by the high-voltage field and a grounded part of the bearing unit of the shaft, the atomizer known from EP 0 796 663 B1 uses a stationary contact ring with carbon-fiber bristles that slide on the rotating shaft to produce an electrically conductive connection. Here, one disadvantage is the wear caused by the mechanical contact. In addition, in practice a contact ring removed to perform maintenance on the bearing unit might not be installed again inadvertently. The results are incorrect potential neutralization and damage to the bearing unit due to spark erosion.
For contact-free grounding of the shaft of an electrostatic rotary atomizer, it is known from EP 1 118 388 A1 to arrange a grounded, adjustable screw in the bearing housing, whose tip faces a peripheral surface of the shaft. This arrangement does not satisfactorily solve the stated problem, because the point discharge at the screw tip leads to deterioration due to spark erosion. Manual adjustment of the screw, which is used to compensate for erosion, is not only troublesome and time-consuming, but also too imprecise for a defined potential neutralization.